Fine spherical powder production during gas atomization of pressurized melts through melt nozzles with a small inner diameter

A pressure-gas atomizer was developed, in which the melts were pressurized through melt nozzles with a small inner diameter, aiming for a small mass median diameter (MMD, d50,3) and high productivity of fine spherical powders. The maximum melt flow resistance in a melt nozzle, defined as the sum of the capillary resistance and viscous pressure drop, was analyzed by varying the inner diameter of the melt nozzle (D0). The calculation results indicate that the maximum melt flow resistance increases quickly with the decrease of D0, and varies in an order of 100–102 kPa for different metal melts when D0 reduces from 4.0 mm to 0.5 mm. Atomization runs with three kinds of aluminium (Al) alloys were accomplished using melt nozzles with different inner diameters in a pilot plant whereby an over-pressure in a range of ∆pl = 30–45 kPa can be maintained on the melts to enhance the melt flowing in the melt nozzle. The experimental results indicate that the atomization efficiency can be well improved by reducing the inner diameter of the melt nozzle, which resulted in a small MMD, narrow particle size distribution and high fine powder yield. For Al-I alloy powders, when the inner diameter of the melt nozzle reduces from D0 = 3 mm to D0 = 1 mm, the particle MMD reduces from d50,3 = 86.13 μm to d50,3 = 40.42 μm, and the powder yield <53 μm increases from 27.60% to 62.57%. For Al-III alloy powders, when the inner diameter of the melt nozzle reduces from D0 = 4 mm to D0 = 2 mm, the particle MMD reduces from d50,3 = 120.10 μm to d50,3 = 54.82 μm and the powder yield <53 μm increases from 20.70% to 48.20%. Moreover, the satellite particles and lamellae sticking on the particle surface were reduced when a melt nozzle with a small inner diameter was employed in a gas atomization process.